Prospective evaluation of latent tuberculosis with interferon-gamma release assays in drug and alcohol abusers

In vitro tests have been developed for the diagnosis of tuberculosis (TB) infection. The objective was to analyse latent TB infection in drug and alcohol abusers through two interferon-gamma techniques. One hundred and thirty-nine patients were admitted between February 2006 and May 2007. Mean age was 39.8 years [31% HIV positive]. The enzyme immunoassay (EIA) and enzyme-linked immunospot (ELISPOT) interferon-gamma assays were positive in 34% of patients with an agreement of 83% (kappa=0.63). Tuberculin skin test (TST) was positive in 29% of patients and the agreement of TST with EIA and ELISPOT interferon-gamma assays was 85% (kappa=0.62) and 83% (kappa=0.57), respectively. Almost 50% of patients with history of TB had a positive in vitro test. In conclusion, we observed a high prevalence of latent TB and good agreement between the new in vitro tests that otherwise may continue to be positive long after developing TB disease.